I was recently gifted a new pair of speakers - a very old pair of Spendor BC1. These were owned by an ex-BBC engineer who acquired them when he retired and held on to them for many years, but a recent downsize meant they needed a new home - and I was happy to provide that home.
These are the active version, BC1a. They're not strictly speaking active speakers, more like passive speakers with amplifiers attached. They have a passive crossover inside instead of an amplifier per driver.
They're very 70's looking. Big and heavy - usually a good thing in a speaker.
They are well known for their midrange and they do sound really good with vocals. They suffer a bit in the bass though - a bit boomy, which is not surprising given the very short port (just a hole in the front baffle) and the reportedly high Qts of the woofer, which probably leads to a peak in the low end response.
Getting them off the ground on some stands is supposed to help, but I'm going to have to make something big and strong enough to hold these up.
The BC1s use an 8" woofer made from Bextrene (a material originally used to make egg boxes) covered with some kind of thick, black stuff. Treble is handled by a Celestion HF1300 tweeter, the same unit used in my Celestion Ditton 10s and a decent tweeter by all accounts, certainly for its age. A Coles 4001 supertweeter fills in the top octave as the Celestion doesn't have much to say for itself above about 15kHz. Apparently the supertweeter was originally added to intentionally make this a 3-way speaker and therefore officially a "professional" product, which avoided Purchase Tax.
The port is just a hole in the front baffle. A recommended upgrade for these is sticking a port tube about 2.5" long into this hole. Something I might try one day.
Walls are fairly thin plywood at 10mm but are heavily damped with some kind of damping sheet about 10mm thick, stuck to the walls with something like bitumen. 30mm thick absorbent foam lines 3 of the sides.
The amplifier set into the back panel is a Spendor M.208. I'm not sure how much power these things produce, but it's probably no more than 25w. Later versions used the M25 or M50 amps (25w and 50w respectively).
Mains power is via an XLR-LNE connector. Audio input is by either balanced "B-gauge" (GPO) jack or a very old style Plessey "Painton" connector (the 4-pin square thing).
The volume pots needed a good clean with Servisol to get rid of some pretty bad crackles. But the amplifiers work fine after that. Quite a bit of hum on them though.
One of the signs that these are an early version of BC1 - the blue alnico magnet on the woofer. Slightly later versions had a red alnico magnet which gave a bit more power handling, which were followed with more modern ceramic magnet woofers. The white surround on the woofer is also an early design and there are reports of these often being perished. There are no signs of that here, although taking the front grille off has to be done from inside on these early models and I've not attempted that yet.
The crossover has 3rd order slopes (apart from the top end of the HF1300 which has no low-pass filter) and crosses at 3kHz and 13kHz. It uses transformers as inductors and what appear to be polypropylene capacitors or similar (some starting to crack due to age, but apparently still working). More info on the crossover and drivers here (for the 1980's version of the speaker).
The M.208 amplifier is a pretty basic affair. Output transistors are mounted on the heatsink behind the PCB. The balanced inputs are converted to single-ended by a transformer (the silver can on the left) and then go through a volume pot into the amp. Some pretty thin gauge wiring is used between the amp and crossover.
To deal with the balanced inputs, the BBC engineer who gave me these speakers had made an unbalanced to balanced converter with BBC LL/76MSC 1:1 transformers. You can see the rather vintage looking General Post Office B-gauge connectors and fabric sleeved cables above.
It will be a lot easier for me to use these speakers with the rest of my hifi if I can use them with my current amplifier. I need to find a way of bypassing the internal amp in a way that is reversible, without making any new holes in the cabinets and ideally switchable so I can choose how to amplify them.
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